Distinct from the all-too-common acrimony between divorcing parents, the syndrome is an internationally recognised phenomenon. In America and Canada, “parenting coordinators” are ordered and supervised by the courts to help restore relationships between parents and children identified as “alienated”. In Mexico and Brazil, alienating a child from a parent is a criminal act.

Psychiatrist Richard Gardner developed the concept 20 years ago, defining it as “a disorder that arises primarily in the context of child custody disputes. Its primary manifestation is the child’s campaign of denigration against a parent, a campaign that has no justification. It results from the combination of a programming (brainwashing) parent’s indoctrinations and the child’s own contributions to the vilification of the target parent.”

The assistant director of Cafcass, Sarah Parsons, said: “Parental alienation is responsible for around 80% of the most intransigent cases that come before the family courts … We already train our social workers to recognise the issue, but this takes helping families experiencing it one step further.”

Miriam, a lecturer and artist, whose name has been changed, was packing to take her young son on holiday when her former husband emailed to say she would never see her child again. The boy was staying with his father for the weekend and, the email said, had made such serious allegations against his mother that he wouldn’t ever be coming home. It would be 592 days before Miriam next saw her son.

“I’m just a normal mum and out of nowhere, I was being accused of false and fabricated allegations of a sexual nature against my son that were absolutely harrowing,” she said. “It was horrendous.”

Since their divorce, seven years previously, Miriam’s former husband had waged a campaign of parental alienation against her, using almost all the 17 specific strategies identified through research studies with adults who were alienated as children and with targeted parents.

These include a parent constantly badmouthing and belittling the other parent to the point that the child sees no value in the targeted parent at all, limiting contact with the targeted parent, forbidding discussion and pictures of them, creating the impression that the targeted parent does not love the child or is dangerous, forcing the child to reject the other parent, and asking the child to spy and keep secrets from them.

Judges in Britain are also increasingly recognising the phenomenon. In one case, the judge wrote about a case where she was forced to transfer residence to re-establish a relationship between a child and an alienated parent. “I regard parental manipulation of children, of which I distressingly see an enormous amount, as exceptionally harmful,” she wrote in her summary.

Joanna Abrahams, head of family law at Setfords Solicitors, is one of only a limited number of lawyers in the UK who specialise in cases of parental alienation. She has seen a steady increase in cases in the past few years.

“Although awareness is increasing, I’m not convinced that judges or social workers have the training and exposure that enables them to identify parental alienation and act on it,” she said. “The only real chance a victim of parental alienation has to get their child back is to find a specialist solicitor who has the expertise to ask the court to order psychological assessments, directed therapy and, if necessary, a change of residence of the child back to the alienated parent.”

These are expensive interventions, however, and cuts to Legal Aid mean parental alienation is something only wealthier parents are likely to have recognised. She said it can cost as much as £50,000 to have parental alienation properly identified.

But Dr Amy Baker, a developmental psychologist, researcher and author of Adult Children of Parental Alienation Syndrome: Breaking the Ties that Bind, says severe parental alienation can poison a child’s mind towards a previously much-loved parent in an alarmingly short period of time.

“When children have become alienated … parents who were once loved and valued seemingly overnight become objects of hatred and fear,” she said. “They appear to feel no loss over the end of the relationship with their parent and are willing to share their views [of hatred] without experiencing any shame or discomfort. Such children would likely be willing to make a false allegation of the other parent.”

This, said Baker, is the difference between an abused child and an alienated one. “Children do not typically reject a parent, even a relatively bad one, unless they have been manipulated to do so,” she said. “Children who have been maltreated are typically quite reluctant to talk about and to admit that was a parent who harmed them. Even once they admit the maltreatment, they are still typically reluctant to reject that parent, often blaming themselves for the abuse instead.”

Karen Woodall, a specialist in parental alienation at the Family Separation Clinic, said there is a “lack of understanding in family courts, professionals and in family services in general”. Cases of severe parental alienation, she said, are rare but “absolutely terrifying”.

“We have a system that doesn’t do what needs to be done in these cases,” she added. “These cases go on for years, with the children getting more and more stuck. We should be applying differentiation at the start: is this rejection by the child justified or not? If not, intensive psychological help needs to be given immediately.”

The silver lining is that all specialists agree that children can recover very quickly, with the right help and, if necessary, separation from the alienating parent.

“I’ve seen it time and time again, even with children who have refused to see their alienated parent for as many as 10 years, or made allegations of horrific sexual abuse and even cannibalism,” said Woodall. “No matter what age the child is, if you put them back into a normal, family environment with the alienated parent, they ‘flip’ back to their former loving selves in an astonishingly short time.”

Miriam, however, is losing hope that she will ever have a meaningful relationship with her son again. The criminal court dismissed the allegations of sexual assault, but after having no contact with his mother during those 592 days, her son will now only consent to supervised visits in a contact centre with his mother every six weeks.

“I have to be prepared for my ex-husband to tell my son that he doesn’t have to see me any more, and the visits to stop,” said Miriam. “My son has been so severely manipulated by his father that it may not be until he has his own children that he comes back to me. But in case he hasn’t come back by the time I die, I’ve put letters and videos for him alongside my will to tell him how much and how unconditionally I love him.

“I try to be hopeful,” she said. “But every night, I go to sleep crying.”

This article was changed on 14th July. It originally stated that the Cafcass was launching a government-funded therapeutic programme. In fact, the support it is offering followed a government pilot programme. The article also originally quoted Joanna Abrahams as saying that identifying parental alienation can cost “upwards of £50,000”. She subsequently corrected her estimate to “as much as £50,000”.